1. Field of the Invention
The present invention relates generally to the fields of neuroendocrinology and the mechanisms involved in stress. More specifically, the present invention relates to novel corticotropin releasing factor-related peptides, urocortin II and human urocortin-related protein, which are involved in the stress response.
2. Description of the Related Art
Corticotropin-releasing factor (CRF) is a 41-amino acid peptide best known for its indispensable role in initiating pituitary-adrenal responses to stress, an effect mediated by type 1 CRF receptors (1). In addition, corticotropin-releasing factor is widely distributed in brain, and has been shown repeatedly to participate in the mobilization of complementary autonomic and behavioral adjustments to a variety of threatening circumstances (2, 3). This has fostered the widely held hypothesis that corticotropin releasing factor and its related family of peptides play important roles in regulation of the hypothalamic-pituitary-adrenal axis (HPA) under basal and stress conditions (4, 5). It is also believed that corticotropin-releasing factor is also involved in other neuroendocrine and paracrine responses in many tissues. Members of the CRF family integrate endocrine, autonomic and behavioral responses to stressors. These peptides may also be implicated in the control of appetite, arousal, and cognitive functions. Severe psychological and physiological consequences can occur as a result of the long term effects of stress, such as anxiety disorders, anorexia nervosa and melancholic depression.
Corticotropin-releasing factor family members mediate their biological actions by specifically binding to CRF receptors with high affinities (6, 7). CRF receptors are G-protein coupled receptors that act through adenylate cyclase and are structurally related to the secretin family. This family also includes GRF, VIP, PTH, and the Calcitonin receptor. The CRF receptor gene has 13 exons and several splice variants of this receptor have been found. The CRF-R1 receptor is distributed throughout the brain and is found in sensory and motor relay sites (8). The CRF-R2α is distributed in lateral septum, ventral medial hypothalamus, nucleus of the solitary tract and the dorsal raphe nucleus, which are areas where CRF-R1 is expressed very little or not at all (9). The CRF-R2β is found mostly in peripheral sites including the heart, blood vessels, gastrointestinal tract, epididymis, lung and skin (7, 10). The pharmacology of the two types of receptors differs in that corticotropin-releasing factor has a low affinity for CRF-R2 (Ki=15-100 nM) but high affinity f or CRF-R1 (Ki=1-2 nM). Other related peptides such as carp urotensin, frog sauvagine, and urocortin have a high affinity for CRF-R2. CRF-R2 knockout mice demonstrate an increased anxiety-like behavior caused by hypersensitivity to stressors (11).
A number of the cell groups identified as sites of peptide action in eliciting stress-like autonomic and behavioral responses have been found to be lacking or impoverished in the expression of requisite ligand(s), receptors or both (12, 13). This has kindled the search for additional CRF-related signaling molecules, which currently number two ligands, G protein-coupled receptors derived from two distinct genes (CRF-R1 and CRF-R2), and a binding protein, whose function remains incompletely understood (14, 15).
A second mammalian CRF-related neuropeptide, urocortin (Ucn), was recently discovered (16) and shown to be bound with high affinity by both known CRF receptor types, whereas CRF is bound in a highly preferential manner by CRF-R1. Centrally administered urocortin is more potent than CRF in suppressing appetite but less so in generating acute anxiety-like effects and generalized behavioral activation (17). This has been taken to indicate that urocortin might mediate some stress-related effects attributed initially to CRF, at least in part by serving as an endogenous ligand for CRF-R2. This view has been challenged, however, by such observations as that the principal cellular seats of urocortin expression in brain are not recognized as integral components of central stress-related circuitry, and that most major sites of CRF-R2 expression are poorly innervated by urocortin-containing projections (18). These and other findings support the possible existence of one or more additional CRF receptor ligands in the mammalian brain.
The prior art is deficient in the lack of recognition of additional urocortin genes and proteins. The present invention fulfills this longstanding need and desire in the art.